Data Model and ERD Flashcards
–person, place, object, event, concept (often
corresponds to a row in a table)
Entities
–link between entities (corresponds to primary
key-foreign key equivalencies in related tables)
Relationships
property or characteristic of an entity or relationship type
(often corresponds to a field in a table)
Attribute
An attribute (or
combination of attributes) that uniquely
identifies individual instances of an entity
type
Identifier(key)
an attribute that
could be a key…satisfies the requirements
for being an identifier
Candidate Identifier
multivalued attribute
{ }
derived attribute
[ ]
The relationship type is modeled as lines between
entity types…the instance is between specific
entity instances
Relationship Types vs. Relationship Instances
combination of relationship
and entity
Associative Entity
is the
number of entity types that
participate in it
Degree of a relationship
Each entity in the relationship will have exactly one
related entity
One-to-one
An entity on one side of the relationship can have
many related entities, but an entity on the other side
will have a maximum of one related entity
One-to-many
Entities on both sides of the relationship can have
many related entities on the other side
Many-to-many
the number of
instances of one entity that can or must be
associated with each instance of another
entity
Cardinality Constraints
If zero, then optional
If one or more, then mandatory
Minimum Cardinality
